1. Field of the Invention
This invention relates to an improved process for the preparation of hydrocarbon oxidation catalyst compositions. More particularly, it relates to a new vanadium (IV) phosphate having a substantially improved intrinsic surface area and to a novel method for its production. Still more particularly, it relates to the production of maleic anhydride from n-butane in a vapor phase process employing the foregoing phosphate catalyst.
2. Prior Art Description
The preparation of mixed oxide compositions of vanadium and phosphorus and the use of these compositions as catalysts in hydrocarbon oxidations is known in the art. The conventional preparative methods are unsatisfactory in that:
(1) they usually require that the process equipment be fabricated of special corrosion-resistant materials of construction; and PA1 (2) they are troubled by serious waste disposal problems. PA1 (1) an intrinsic surface area in the range 10 to 100 square meters per gram (BET Method); PA1 (2) a phosphorus to vanadium atomic ratio of about 1 to 1; and PA1 (3) an average valence for the vanadium in the composition in the range plus 4.0 to plus 4.5. PA1 (1) of vanadium and oxygen; or PA1 (2) of vanadium, oxygen and hydrogen; or PA1 (3) of vanadium, oxygen, hydrogen and carbon. PA1 (1) that the compound does not set (polymerize) or decompose when in contact with phosphoric acid at the temperature of use; and PA1 (2) as a practical matter, little or none of the compound reacts with phosphoric acid at the temperature of use. PA1 (1) The dried solid is heated to 380.degree. C. in a stream of air flowing at 1.5 vol/vol/min. The heat input should yield a rate of temperature increase of about 3.degree. C. per minute. PA1 (2) The 380.degree. C. temperature is then maintained and the same air flow rate continued for about 2 hours. PA1 (3) The temperature is then increased from 380.degree. C. to 480.degree. C. at the 3.degree. C. per minute rate of increase while passing in air-butane mixture, 1.5 volume percent of butane in air, through the bed (121/2 inch by 3/4 inch diameter tube) at a flow rate of 2-3 vol/vol/min. PA1 (4) The 480.degree. C. temperature is maintained for about 15 hours while continuing the air-butane flow rate as before. PA1 (5) The temperature is then reduced from the 480.degree. C. value to 420.degree. C. and the air-butane flow rate is increased to a VHSV of 1,000 hrs..sup.-1 (17 vol/vol/min.). PA1 (6) Finally the temperature is adjusted upward or downward, as required, to achieve the desired degree of butane conversion. PA1 (1) vanadium and oxygen; PA1 (2) vanadium, oxygen and hydrogen; or PA1 (3) vanadium, oxygen, hydrogen and carbon PA1 (1) to facilitate removal of water from the medium by azeotropic distillation; PA1 (2) to partially replace more costly hydroxylic liquid components; and PA1 (3) to reduce the polarity of the reaction medium.
These difficulties arise from the employment of hydrogen chloride or oxalic acid for the dissolution of the vanadium component.
The known mixed oxide compositions, in general, suffer from a number of disadvantages which include relatively poor selectivities and activities as catalysts in the partial oxidation of a saturated hydrocarbon feed, for example n-butane to maleic anhydride, and the like oxidations with molecular oxygen.
Representative descriptions in the art which relate to the production of maleic anhydride from n-butane include U.S. Pat. No. 3,293,268.